1. Field of the Invention
The present invention relates to a method of determining the type of plastics. More particularly, the present invention relates to a method of determining the type of plastics, which, in disposing of or recycling diverse waste of plastics such as plastic bottles for soft drink and plastic packages of foods, is adapted to be used for classifying plastic waste by materials.
2. Prior Art
Various types of plastics including plastic bottles for soft drink and plastic packages of foods are rejected as waste after use in large quantities and are disposed of by incineration or dumping for reclamation.
A problem is however that incineration is not suitable for some types of plastics because the incinerator is damaged, and it is becoming more and more difficult to find new incinerating yards and land for reclamation. It is therefore tried now to manufacture petroleum and other fuel from plastic waste, or to recycle waste by bringing back to the original plastic materials for each type of plastics.
Under such circumstances, it is becoming more important than ever to determine the type of plastics and classify plastic waste into individual types.
The conventional methods already in industrial use for classifying plastics include a method using the difference in specific gravity between different types of plastics and a method of identifying polyvinyl chloride based on X ray.
In the method based on specific gravity, however, separation is difficult between polyethylene and polypropylene and between polyvinyl chloride and polyethylene terephthalate, because of the relatively slight difference in specific gravity, and another problem is that specific gravity of plastics varies as a result of surface wetting of plastics or kneading with pigment or filler, so that these methods are far from being satisfactory.
In the method based on X ray also, use of radiation poses problems in safety and management, and in addition, polyvinyl chloride is the only plastics that this method can identify and classify, so that this cannot be practicable.